I have a 1970 cutlass S 455 4 speed. I want posi which it is not. How do I know if its 30 spline or 28. Then when I convert should I replace axel bearings and seals also?

 

to be SURE, pull axle and COUNT

I just heard yesterday of a did that "should have" one spline count but was fitted with the other count spiders instead.

Be certain. Count.

 

As well, check with Supercars Unlimited (www.supercarsunlimited.com) for availability of kits to convert to limited slip. I updated my '69 4-4-2 from a 3.23 open to a 3.23 limited slip using the kit available from Supercars and it worked great!

Randy C.

 

I get most of my rear end parts from DTS. (Drive Train Specialists) When I put a posi in my 10 bolt, they not only wanted the spline count but also the number of bolts in the ring gear. Like Octania said, just do the count.

 

If it's the original rear, it should be a 28 spline Type-O rear end (unless it's a Canadian built car then it could have come with a Chevy 12 bolt). The 31 spline (not 30 spline) HD Type-O rears were last used in 1968. Then again, after 45 years there could be some other rear end so you need to verify what you have prior to purchasing any parts.

There are new posi units for the Type-O that are machined Ford 8.8 posi units, which are a drop in replacement for 3.08-3.23 gear ratios (I think but you need to verify this). If you have some other ratio you will need a ring gear spacer or a factory LSD.

Since you have to pull the axle shafts in order to remove the carrier, axle bearing and seal replacement is a no brainer.

 

He said it is a 1970. No Olds built at Oshaw CA after 1969 so the Chevy 12 bolt is not part of the discussion.

 

Thanks, I wasn't aware of the Canadian build specifics.